The present invention relates generally to the fields of biology, chemistry and medicine. More particularly, it concerns derivatives of potassium channel inhibitors, including derivatives of 4-aminopyridine, and methods of making and using thereof, including for the medical imaging of neurodegenerative conditions.
With nearly 400,000 people affected in the U.S. and 2.5 million worldwide, Multiple Sclerosis (MS) is the most common neurodegenerative condition in young adults (Calabresi, 2007). The progressive demyelination of neurons in the brain leads to diverse neurological symptoms. Myelin is the multilayered membrane that surrounds most axons of the central and peripheral nervous systems and is essential for the propagation of rapid nerve impulses. In people with MS, the myelin sheath that normal covers the axons is lost and this leads to aberrant leakage of potassium ions from the axon and improper impulse conduction.
One approach to treat MS or to mitigate the symptoms associated with MS is to block potassium channels to reduce the leakage of potassium ions, thus enhancing impulse conduction. In January 2010, the FDA approved 4-aminopyridine (4-AP), as a therapy for MS (Ampyra, Acorda Therapeutics, Inc., 2010). 4-AP is a relatively selective blocker of Kv1 family of K+ channels (Wulff et al., 2009). By blocking K+ channels, impulse conduction along the axon is partially restored and symptoms ameliorate.
To develop new neuroprotective therapies for MS or other neurodegenerative diseases, it is essential to have proper tools to diagnose and assess disease progression.
Currently, the diagnosis of MS and the evaluation of disease progression are based on clinical evaluation and the presence of certain non-specific signals on a gadolinium-enhanced MRI (Olek, 2011). Unfortunately, the wide array of symptoms associated with the disease (i.e.: numbness, vision loss, limb weakness, coordination problems, pain, etc.) makes establishing universal clinical metrics that could be used in clinical trials a difficult task. In addition, the lesions observed in a gadolinium-enhanced MRI are mainly indicative of inflammation, which in most cases is transient and poorly informative of disease progression. Specific pyridine compounds for use in the treatment of injured mammalian nerve tissue are disclosed in
Thus, there is a pressing need for accurate methods to evaluate neurological changes in patients with MS or other neurodegenerative disease. It is also desirable to develop new compounds that are effective in treating MS and other pathologies.
The present disclosure provides novel compounds, including compounds that bind to potassium channels, methods for their manufacture, and methods for their use, including for in vivo imaging of the central nervous system to diagnose and/or assess the progression of MS or other diseases.
Specifically, the present invention concerns an imaging agent comprising the compound of formula (I):
In one aspect, the isotope of fluorine is a radioactive isotope. In particular aspect, the fluorine isotope is 18F. In some aspects, any of C, N, O is optionally replaced by an isotope thereof. An isotope of C, N, O may be any known C, N, O isotope. In particular aspects, the isotope is a radioisotope. For example, any of C, N, O may be optionally replaced by the isotope 11C, 13N, 15O, respectively.
In further embodiments, at least one of R1, R3, is not hydrogen, when R2 is NH2, CH2OH, a nonradioactive fluorine, or CF3. In certain aspects, at least one of R1, R2, and R3 is not hydrogen, when R4 is NH2, CH2OH, a nonradioactive fluorine, or CF3.
In some embodiments, the compounds have the following formulas:
In certain embodiments, there are provided compounds of formula (II):
In certain embodiments, M is CH2F, or (CH2)2F. In further embodiments, M is 18F, CH218F, or (CH2)218F, preferably [18F]-3-fluoro-4-aminopyridine, [18F]-3-fluoro-methyl-4-aminopyridine, or [18F]-3-fluoroethyl-4-aminopyridine. In some aspects, any of C, N, O is optionally replaced by an isotope thereof. An isotope of C, N, O may be any known C, N, O isotope. In particular aspects, the isotope is a radioisotope. For example, any of C, N, O may be optionally replaced by the isotope 11C, 13N, 15O, respectively.
In certain embodiments, there are provided compounds of formula (III):
Also disclosed are compounds of formula (IV):
In some aspects, any of C, N, O in the compounds described herein is optionally replaced by an isotope thereof. An isotope of C, N, O may be any known C, N, O isotope. In particular aspects, the isotope is a radioisotope. For example, any of C, N, O in the compounds of formula (I)-(IV) may be optionally replaced by the isotope 11C, 13N, 15O, respectively.
Pharmaceutical compositions are also disclosed comprising one or more of the above compounds and a pharmaceutically acceptable carrier. In some embodiments, the pharmaceutical compositions further comprise one or more pharmaceutically acceptable excipients. In some embodiments, the composition is formulated for controlled release of any of the compounds disclosed herein.
A kit is also disclosed comprising one or more of the above compounds.
The present invention further concerns an imaging agent of the present invention for use in a method for detecting a demyelinated region in an axon in a subject, in particular wherein the compound blocks potassium channels located at the demyelinated region in an axon in the subject.
In certain embodiments, the imaging is effected by a radiodiagnostic method. The radiodiagnostic method may be performed by any instrument capable of detecting radiation by the compounds. Exemplary radiodiagnostic methods include, but not limited to, Positron Emission Tomography (PET), PET-Time-Activity Curve (TAC) or PET-Magnetic Resonance Imaging (MRI). In particular aspect, the radiodiagnostic method is PET.
Certain embodiments are directed to an imaging agent comprising [18F]-3-fluoro-4-aminopyridine, [18F]-3-fluoro-methyl-4-aminopyridine, or [18F]-3-fluoro-ethyl-4-aminopyridine.
A kit is again disclosed comprising one or more of the above compounds. In further aspects, there are provided a kit comprising one or more of the above compounds comprising a radioisotope.
Methods of treating a demyelinating disease or mitigating a symptom of a demyelinating disease are additionally disclosed comprising administering to a subject in need thereof an effective amount of a compound as defined above. It is specifically contemplated that in certain embodiments, methods related to therapy and/diagnostics involve a subject that is a human patient.
"Treatment" or "treating" includes (1) inhibiting a disease in a subject or patient experiencing or displaying the pathology or symptomatology of the disease (e.g., arresting further development of the pathology and/or symptomatology), (2) ameliorating a disease in a subject or patient that is experiencing or displaying the pathology or symptomatology of the disease (e.g., reversing the pathology and/or symptomatology), and/or (3) effecting any measurable decrease in a disease in a subject or patient that is experiencing or displaying the pathology or symptomatology of the disease.
"Effective amount" or "therapeutically effective amount" or "pharmaceutically effective amount" means that amount which, when administered to a subject or patient for treating a disease, is sufficient to effect such treatment for the disease. In some embodiments, the subject is administered at least about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 mg/kg (or any range derivable therein).
The amount of the compound that is administered or taken by the patient may be based on the patient's weight (in kilograms). Therefore, in some embodiments, the patient is administered or takes a dose or multiple doses amounting to about, at least about, or at most about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7. 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0. 19.5, 20.0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, 350, 355, 360, 365, 370, 375, 380, 385, 390, 395, 400, 410, 420, 425, 430, 440, 441, 450, 460, 470, 475, 480, 490, 500, 510, 520, 525, 530, 540, 550, 560, 570, 575, 580, 590, 600, 610, 620, 625, 630, 640, 650, 660, 670, 675, 680, 690, 700, 710, 720, 725, 730, 740, 750, 760, 770, 775, 780, 790, 800, 810, 820, 825, 830, 840, 850, 860, 870, 875, 880, 890, 900, 910, 920, 925, 930, 940, 950, 960, 970, 975, 980, 990, 1000 micrograms/kilogram (kg) or mg/kg, or any range derivable therein. In some aspects, the pharmaceutically effective amount comprises a dose from about 0.0001 mg/kg/day to about 100 mg/kg/day. In further aspects, the effective amount comprises a dose from about 0.01 mg/kg/day to about 5 mg/kg/day. In still further aspects, the dose is about 0.25 mg/kg/day.
The composition may be administered to (or taken by) the patient 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more times, or any range derivable therein, and they may be administered every 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 hours, or 1, 2, 3, 4, 5, 6, 7 days, or 1, 2, 3, 4, 5 weeks, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 months, or any range derivable therein. It is specifically contemplated that the composition may be administered once daily, twice daily, three times daily, four times daily, five times daily, or six times daily (or any range derivable therein) and/or as needed to the patient. Alternatively, the composition may be administered every 2, 4, 6, 8, 12 or 24 hours (or any range derivable therein) to or by the patient.
In some embodiments, the compounds described herein are comprised in a pharmaceutical composition. In further embodiments, the compounds described herein and optional one or more additional active agents, can be optionally combined with one or more pharmaceutically acceptable excipients and formulated for administration via epidural, introperitoneal, intramuscular, cutaneous, subcutaneous or intravenous injection. In some aspects, the compounds or the composition is administered by aerosol, infusion, or topical, nasal, oral, anal, ocular, or otic delivery. In further embodiments, the pharmaceutical composition is formulated for controlled release.
"Pharmaceutically acceptable" means that which is useful in preparing a pharmaceutical composition that is generally safe, non-toxic and neither biologically nor otherwise undesirable and includes that which is acceptable for veterinary use as well as human pharmaceutical use.
"Pharmaceutically acceptable salts" means salts of compounds of the present invention which are pharmaceutically acceptable, as defined above, and which possess the desired pharmacological activity. Such salts include acid addition salts formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like; or with organic acids such as 1,2-ethanedisulfonic acid, 2-hydroxyethanesulfonic acid, 2-naphthalenesulfonic acid, 3-phenylpropionic acid, 4,4'-methylenebis(3-hydroxy-2-ene-1-carboxylic acid), 4-methylbicyclo[2.2.2]oct-2-ene-1-carboxylic acid, acetic acid, aliphatic mono- and dicarboxylicacids, aliphatic sulfuric acids, aromatic sulfuric acids, benzenesulfonic acid, benzoic acid, camphorsulfonic acid, carbonic acid, cinnamic acid, citric acid, cyclopentanepropionic acid, ethanesulfonic acid, fumaric acid, glucoheptonic acid, gluconic acid, glutamic acid, glycolic acid, heptanoic acid, hexanoic acid, hydroxynaphthoic acid, lactic acid, laurylsulfuric acid, maleic acid, malic acid, malonic acid, mandelic acid, methanesulfonic acid, muconic acid, o-(4-hydroxybenzoyl)benzoic acid, oxalic acid, p-chlorobenzenesulfonic acid, phenyl-substituted alkanoic acids, propionic acid, p-toluenesulfonic acid, pyruvic acid, salicylic acid, stearic acid, succinic acid, tartaric acid, tertiarybutylacetic acid, trimethylacetic acid, and the like. Pharmaceutically acceptable salts also include base addition salts which may be formed when acidic protons present are capable of reacting with inorganic or organic bases. Acceptable inorganic bases include sodium hydroxide, sodium carbonate, potassium hydroxide, aluminum hydroxide and calcium hydroxide. Acceptable organic bases include ethanolamine, diethanolamine, triethanolamine, tromethamine, N-methylglucamine and the like. It should be recognized that the particular anion or cation forming a part of any salt of this invention is not critical, so long as the salt, as a whole, is pharmacologically acceptable. Additional examples of pharmaceutically acceptable salts and their methods of preparation and use are presented in
In certain embodiments, the demyelinating disease includes, but is not limited to, multiple sclerosis, spinal cord compression, ischemia, acute disseminated encephalomyelitis, optic neuromyelitis, leukodystrophy, progressive multifocal leukoencephalopathy, metabolic disorders, toxic exposure, congenital demylinating disease, peripheral neuropathy, encephalomyelitis, central pontine myelolysis, Anti-MAG Disease, Guillain-Barre syndrome, chronic inflammatory demyelinating polyneuropathy, or multifocal motor neuropathy (MMN). In particular embodiments, the demyelinating disease is multiple sclerosis.
In additional embodiments, leukodystrophy includes, but is not limited to, adrenoleukodystrophy, Alexander's Disease, Canavan Disease, Krabbe Disease, Metachromatic Leukodystrophy, Pelizaeus-Merzbacher Disease, vanishing white matter disease, Refsum Disease, Cockayne Syndrome, Van der Knapp Syndrome, or Zellweger Syndrome.
Also disclosed are methods for diagnosing a demyelinating disease or evaluating the progression of a demyelinating disease comprising administering to a subject in need thereof the imaging agent described herein and detecting the compound comprised in the imaging agent in the subject. In certain aspects, the compound is detected by a radiodiagnostic method, including, but not limited to PET, TAC, or PET-MRI. In particular aspects, the compound is detected by PET.
In some aspects, the subject is a mammal. In particular aspects, the subject is a human. In additional aspects, the subject is a healthy individual. In further aspects, the subject is a verified or putative animal model of myelin-associated neuropathy. For example, in some embodiments, the animal model is DTA model, cuprizone-induced demyelination model, a lysolecithin injection model or experimental autoimmune encephalomyelitis (EAE) model. In still further aspects, the animal model is a mouse mutant with altered nodal environ, including, but not limited to, shiverer, trembler, jimpy, P0 null, E-cadherin null, Mag null, Dystrophic laminin α2, Cgt null, Contactin null, Caspr null, Cst null, Caspr2 null, Tag1 null, Dystroglycan, quivering Spectrin βIV, Nrcam null, and Na+ channel β2 null.
In some embodiments, the present invention concerns methods for synthesizing the compounds described herein. For example, in said methods the protection group is Boc (N-tert-butoxycarbonyl). In further aspects, the fluoro-containing reagent is XtalFluor E ((Diethylamino)difluorosulfonium tetrafluoroborate).
Specifically, the present invention concerns a method for producing the [18F]-3-fluoro-4-aminopyridine imaging agent of the present invention, comprising the steps of: (a) converting 4-(Boc-amino)pyridine to an intermediate compound, and (b) fluorinating the intermediate structure B to form [18F]-3-fluoro-4-aminopyridine, (c) removing Boc to form the [18F]-3-fluoro-4-aminopyridine imaging agent, wherein a [18F]-containing reagent is supplied in the fluorination step, in particular wherein the intermediate compound is further defined as:
wherein the [18F]-containing reagent is selected from the group consisting of [18F]-F2, [18F]-AcOF, [18F]F-TEDA, [18F]-Benzo[h]quinolinyl (tetrapyrazolylborate) Pd(IV) fluoride trifluoromethanesulfonate. For example, [18F]-3-fluoro-4-aminopyridine is produced by a method comprising (a) converting a compound having the structure A (4-(Boc-amino)pyridine) to an intermediate compound with structure B, and (b) fluorinating the intermediate structure B to form [18F]-3-fluoro-4-aminopyridine. A [18F]-containing reagent is supplied in the fluorination step.
The present invention also concerns a method for producing the [18F]-3-fluoro-4-aminopyridine imaging agent of the present invention, comprising the steps of: (a) using Koser's reagent to iodonate 4-(Boc-amino)pyridin-3-ylboronic acid to form a first intermediate compound, (b) fluorinating the intermediate compound by using a [18F]fluor-containing reagent, and (c) using HCl to remove the protecting group to yield [18F]3-fluoro-4-aminopyridine imaging agent.
The present invention additionally provides a method for producing [18F]-3-fluoromethyl-4-aminopyridine, comprising the steps of: (a) protecting the amino group of 4-aminopyridine-3-methanol with a Boc to form a first intermediate compound, (b) converting the hydroxyl group to a mesylate to form a second intermediate compound, (c) fluorinating the second intermediate compound by using a [18F]-containing reagent to form a third intermediate compound, and (d) removing the protection group from the third intermediate compound to form [18F]-3-fluoromethyl-4-aminopyridine, wherein the [18F]-containing reagent is [(crypt-222)K]+ 18F-.
In an additional aspect, [18F]-3-fluoroethyl-4-aminopyridine may be synthesized by a method comprising the steps of: (a) protecting the amino group of 4-aminopyridine-3-ethanol with a protection group to form an intermediate product, (b) fluorinating the intermediate product by using a [18F]-containing reagent, in particular the [18F]-containing reagent Xtal Fluor E ((Diethylamino)difluorosulfonium tetrafluoroborate, and (c) removing the protection group to form the [18F]-3-fluoroethyl-4-aminopyridine imaging agent.
In certain embodiments, the [18F]-containing reagent includes, but is not limited to, [18F]-Kryptofix, [18F]-F2, [18F]-AcOF, [18F]F-TEDA, [18F]-Benzo[h]quinolinyl (tetrapyrazolylborate) Pd(IV) fluoride trifluoromethanesulfonate, [18F]-2-fluoroethyl bromide, and [18F]-fluoromethyl- bromide. In particular aspects, the [18F] containing reagent is [18F] Kryptofix.
An alternative method for producing [18F]3-fluoro-4-aminopyridine comprises the step of using Koser's reagent to iodonate 4-(Boc-amino)pyridin-3-ylboronic acid to form a first intermediate compound, as described above.
The methods for producing the compounds described herein are not limited to the exemplary methods described herein. The compounds may be synthesized by any suitable method known in the art and it will be obvious to those skilled in the art that various adaptations, changes, modifications, substitutions, deletions or additions of procedures may be made within the scope of the appended claims.
Also disclosed is the use of a compound discussed herein for research purposes involving a potassium channel blocker. The compound may be used for its potassium channel blocking activity. Therefore, such methods involve exposing, contacting, or adding a compound discussed herein to a channel or a polypeptide involved in channel activity and determining calcium channel activity. In some embodiments, the compound is a control. In other embodiments, the compound is used to screen other compounds for an activity that affects channel activity (such as by inhibiting or enhancing that activity).
Because of the biological activity of the compounds disclosed herein, in additional embodiments, there are methods and compositions disclosed for use of these compounds as an avicide. In some embodiments, a compound discussed herein is formulated as grain bait, a powder concentrate or a liquid for exposure to or ingestion by birds. The LD50 for birds is generally in the range of about 100 parts per million (ppm) to 1000 parts per million, and dosages are formulated to provide at least that much to birds. Embodiments also include methods of using an avicide comprising providing to an avian an effective amount of a composition comprising a compound discussed herein, including but not limited to those having Formula I or Formula II. In certain embodiments, providing the compound comprises distributing the composition to places that birds can access, including but not limited to distributing it in grass, trees, bushes, on leaves, in bird feeders or in bird baths or other food or water supplies for birds. In further embodiments, distributing the composition may involve spraying a liquid or powder composition, or depositing or placing a solid, liquid or powder composition. In certain embodiments, a subject is a bird.
Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the measurement or quantitation method.
The use of the word "a" or "an" when used in conjunction with the term "comprising" may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."
The words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.
The compositions and methods for their use can "comprise," "consist essentially of," or "consist of" any of the ingredients or steps disclosed throughout the specification. Compositions and methods "consisting essentially of" any of the ingredients or steps disclosed limits the scope of the claim to the specified materials or steps which do not materially affect the basic and novel characteristic of the claimed invention.
It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Note that simply because a particular compound is ascribed to one particular generic formula doesn't mean that it cannot also belong to another generic formula.
Figs. 1A-1C illustrate the mechanism of action of a potassium channel blocker. (A) shows a scheme of a healthy neuron. (B) shows a scheme of a demyelinated neuron. Aberrant leakage of potassium ions from the axon results in poor conduction of electrical impulses along the axon. (C) shows a demyelinated neuron treated with a potassium channel blocker.Figs. 2A-2G show potassium channel blockers and fluorinated 4-AP derivatives. (A) 4-aminopyridine (B) 3,4-diaminopyridine (C) 3-methanol-4-aminopyridine (D) 3-fluoro-4-aminopyridine (E) 3-fluoromethyl-4-aminopyridine (F) 3-fluoroethyl-4-aminopyridine (G) 2-fluoro-4-aminopyridineFigs. 3A-3F . (A) shows synthesis of 3-fluoromethyl-4-aminopyridine. (B) shows synthesis of 3-fluoroethyl-4-aminopyridine. (C) shows NMR of 3-fluoromethyl-4-aminopyridine. (D) shows high resolution Mass Spectra of 3-fluoromethyl-4-aminopyridine. (E) shows NMR of 3-fluoroethyl-4-aminopyridine. (C) shows high resolution Mass spectra of 3-fluoroethyl-4-aminopyridine.Figs. 4A-C show enhancement of compound action potential (CAP) by 4-AP derivatives. (A) CAP traces before (solid line) and after (dashed line) addition of the drug. Scale bar: 5 mV / 5 ms. (B) Relative increase of maximum CAP amplitude vs. concentration for each drug. Amplitude was normalized to the amplitude before the drug. (C) Half-maximal effective concentration of each molecule and 95% confidence interval obtained from fitting the data to the Hill equation, n = number of times each drug was tested.Figs. 5A-C show inhibition of ionic current of Shaker K+ channel by 4-AP derivatives. (A) K+ currents were generated by a series of 50 ms pulses from -70 mV to +40 mV in increments of 10 mV in the presence of cumulative concentrations of 4-AP derivatives. Each panel represents the K+ current recorded from the same oocyte before and after addition of the drug. Scale bar: 1 µA / 10 ms. (B) Relative K+ current vs. concentration for each drug obtained at +20 mV. (C) Half-maximal inhibitory concentration of each molecule and 95% confidence interval obtained from fitting the data to the Hill equation, n = number of times each drug was tested.Figs. 6A-B show pharmacology of 4-AP derivatives. (A) Pharmacological parameters for 4-AP derivatives and control compounds. cLogP: calculated partition coefficient using VCCLAB (I. V. Tetko et al., Virtual computational chemistry laboratory-design and description. Journal of computer-aided molecular design 19, 453 (Jun, 2005 Figs. 7A-D. Brain distribution of 4-AP in mice injected with LPC. Top label represents mouse name + section number. A: Fluorescent microscopy of myelin basic protein (MBP) immunostaining. Each small square represents one picture at 40X. Areas rich in MBP appear darker. Partial demyelination is evident in certain areas of the corpus callosum. B: Autoradiography: areas where 4-AP localizes appear darker. 4-AP mostly localizes in grey matter areas with almost no signal in white mater areas. C and D: 2x magnification of the corpus callosum area from A and B. Areas of demyelination in the corpus callosum appear darker than the rest of the corpus callosum. The corpus callosum has been marked with a dashed white line and the areas of demyelination within the corpus callosum have been circled with a solid white line. Autoradiographic signal is more intense in areas of demyelination compared to the rest of the corpus callosum. Scale bar = 2 um. All animals pictured here received LPC injections however not all of them showed lesions at the level of sectioning (ie. no lesions are observed in LPC1-12).Fig. 8 . Possible radiosynthesis of [18F] 3-F-4-AP and [18F] 3-MeF-4-AP
Multiple sclerosis (MS) is the most common neurodegenerative disease in young adults. The progressive demyelination of neurons in the central nervous system (CNS) is the hallmark of MS (Calabresi, 2007). When axons lose their myelin, K+ channels in the axonal membrane become exposed and leak K+ ions (
4-aminopyridine (4-AP) and 3,4-diaminopyridine (3,4-DAP) are well-known potassium channel blockers relatively selective for voltage gated K+ channels of the Kv1 family (Wulff et al., 2009). 4-AP sensitive K+ channels, Kv1.1 and Kv1.2, are localized in the juxtaparanodal region of myelinated axons. Upon demyelination these channels redistribute throughout the intermodal region of the axons as seen in tissue samples from MS patients and in demyelinated animals. In demyelinated animals Kv1 channels have been shown to be upregulated 2-4 fold. 4-AP and 3,4-DAP have been used effectively in the treatment of Lambert-Eaton Syndrome and Multiple Sclerosis (Murray and Newsom-Davis, 1981; Soni and Kam, 1982; Lundh et al., 1977). 4-AP and 3,4-DAP block Kv1 Potassium channels with affinities in the micromolar range. Binding of 4-AP and 3,4-DAP to Kv1 potassium channels restores impulse conduction in demyelinated fibers (Yeh et a/., 1976; Sherratt et al., 1980; Kirsch and Narahashi, 1978). 4-aminopyridine-3-methanol can also restore impulse conduction of demyelinated fibers (Sun et al., 2010; Leung et al., 2011).
In January 2010, the FDA approved a slow-release formulation of 4-aminopyridine (4-AP), to improve walking in MS patients (Ampyra, Acorda Therapeutics, Inc., 2010). 4-AP is a relatively selective blocker of Kv1 family of K+ channels (Wulff et al., 2009). The proposed mechanism of action of 4-AP in MS patients is that 4-AP blocks K+ channels in demyelinated axons, which leads to improved impulse conduction (http://goo.gl/fqcZo).
Fluorinated molecules generally display better pharmacological properties such as increased membrane permeability and metabolic stability than their non-fluorinated analogs. Described herein are compounds of formula I or II, which contain fluorine and efficiently block voltage gated potassium channels. In particular, certain embodiments are directed to fluorinated 4-AP derivatives, such as 3-fluoromethyl-4-ammopyridine, or 3-fluoroethyl-4-aminopyridine.
In addition, 4-AP and 3,4-DAP can efficiently cross the blood brain barrier. Application of a computational model for the estimation of logBB (a parameter used to predict blood brain barrier permeability by certain compounds) predicts that the compounds described herein, in particular, fluorinated 4-AP derivatives, will efficiently cross the blood brain barrier (Sun, 2004). It has also been shown that 3-F-4-AP is more lipophylic than 4-AP (Arzneimittelforschung, 1989)
4-AP is safe within the concentrations used in therapy, which indicates that the compounds described herein, in particular, fluorinated 4-AP derivatives are likely to be safe tools when used in humans.
To effectively treat a patient with a neurodegenerative disease, such as MS, it is important to diagnose and evaluate the progression of the disease in the patient. Currently, magnetic resonance imaging (MRI) is the primary imaging techniques for the diagnosis and the assessment of disorders that disrupt the myelin sheath, including MS. Unfortunately, signal changes on an MRI are non-specific and correlate only indirectly with the underlying pathology. Moreover, current methods do not correlate well with the underlying pathology of the disease and are not well-suited for use in clinical trials.
PET is a non-invasive medical imaging technique that relies on the detection of radiation emitted by a radionuclide (radioactive tracer) introduced in the body of the subject on a biologically active molecule. Images of the radioactive tracer's localization can be reconstructed by computer analysis providing quantitative maps of the radioactive tracer's distribution in the body of the subject. Such images can provide valuable information of the biochemistry and physiology of a subject. Because PET is a molecular imaging technique, it can detect cellular abnormalities before anatomical changes have occurred. For example, 18F-fluorodeoxyglucose (FDG) is widely used to distinguish highly metabolically active cancer cells from other cells (Oriuchi et al., 2006). Similarly, it is conceivable that a "PET-active" molecule that selectively localizes to demyelinated axons could provide accurate maps of the lesions early in the process.
The most common radioisotopes used in PET are 18F, 15O, 13N and 11C, with half-lives of 110, 2, 10, and 20 min respectively. 18F is usually preferred due to its longer half-life and its lower positron energy which results in better resolution. Despite the relatively short half-life of these radioisotopes, they are widely used in medical diagnostics as many hospitals have their own cyclotron to prepare the radioactive tracers or have a nearby facility that can prepare the radioactive tracers.
A recent review on PET markers for MS highlighted several potential targets for PET imaging including 18kDa Translocator Protein, Cannabinoid Receptor Type 2, Myelin, Cerebral metabolic rate of glucose utilization, Type A γ-aminobutyric acid, and Acetyl choline receptor (Owen et al., 2011). Nevertheless, all of these markers have limitations: some of these tracers were originally developed for other conditions and suffer from low pathological specificity; others were developed to target myelin or myelin related proteins and have limited signal-to-noise ratio and the rest target inflammatory cells which do not necessarily correlate with the underlying demyelination. More recently, a report on [11C]PIB, a PET radioactive tracer that binds to amyloid plaques originally developed for Alzheimer's Disease, has been shown to be useful in quantifying myelin (Stankoff et al., 2011). Nevertheless, since MS is a de-myelinating disorder, it would be desirable to have access to a PET radioactive tracer specific for de-myelinated axons. In particular, it would be desirable to develop a PET radioactive tracer that targets potassium channels for imaging demyelination or other conditions.
Incorporation of a positron emitting radionuclide such as 18F into a potassium channel blocker, such as a 4-AP derivative, allows visualization of the location and abundance of exposed potassium channels and provides a better assessment of demyelinated regions. The fact that 4-AP has proven therapeutically beneficial indicates that it preferentially binds to potassium channels of demyelinated neurons. Furthermore, the fact that there are relatively few side effects of 4-AP indicates that there are few off-target receptors at the concentrations currently used in therapy. Such properties indicate that the compounds described herein are suitable for imaging demyelinated neurons with adequate signal-to-noise ratio.
Furthermore, the metabolic stability of [18F]Fluoroalkylbiphenyls, which share a similar core structure to the compounds described herein, have been examined and were found to be stable for PET studies (Lee et al., 2004), indicating that the compounds described herein are likely stable for PET studies.
Substitution of 18F for OH or H is common in the art. Such substitutions generally preserve the biological properties of the molecule and render the molecules suitable for imaging using PET or SPECT cameras. For example substitution of the OH in position 2 of glucose with 18F does not alter the capability to be uptaken by cells. Many examples of 18F substitutions that preserve the parent molecule's properties can be found on the MICAD database (available on the world wide web at ncbi.nlm.nih.gov/books/NBK5330/).
Disclosed herein are new radioactive tracers for PET, which serve as novel diagnostic markers to image demyelinated axons in a subject. In particular embodiments, the new radioactive tracers for PET are 18F-labeled versions of 4-AP derivatives. Methods for their manufacture and methods for their use in in vivo imaging of the central nervous system to diagnose and/or assess the progression of MS or other diseases are also provided. The present disclosure also provides fluorine containing compounds that bind to potassium channels, methods for their manufacture and methods for their use in the treatment of neurodegenerative diseases.
The term "radioactive isotope" refers to an isotope having an unstable nucleus that decomposes spontaneously by emission of a nuclear electron, positron, or helium nucleus and radiation, thus achieving a more stable nuclear composition.
The term "deuterated version" as used herein means one or more of hydrogen in a compound is replaced with 2H, an isotope of hydrogen.
As used herein, the term "radioactive tracer", or "radioactive label", or "tracer", or "radiotracer" means a chemical compound in which one or more atoms have been replaced by a radioisotope. By virtue of its radioactivity, it can be used to explore the mechanism of chemical reactions by tracing the path that the radioisotope follows from reactants to products. A radioactive tracer can also be used to track the distribution of a substance within a natural system such as a cell or tissue. Radioactive tracers form the basis of a variety of imaging systems, such as PET scans and SPECT scans.
The use of the word "a" or "an," when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."
The term "hydrate" when used as a modifier to a compound means that the compound has less than one (e.g., hemihydrate), one (e.g., monohydrate), or more than one (e,g., dihydrate) water molecules associated with each compound molecule, such as in solid forms of the compound.
An "isomer" of a first compound is a separate compound in which each molecule contains the same constituent atoms as the first compound, but where the configuration of those atoms in three dimensions differs.
As used herein, the term "patient" or "subject" refers to a living mammalian organism, such as a human, monkey, cow, sheep, goat, dog, cat, mouse, rat, guinea pig, or transgenic species thereof. In certain embodiments, the patient or subject is a primate. Non-limiting examples of human subjects are adults, juveniles, infants and fetuses.
As generally used herein "pharmaceutically acceptable" refers to those compounds, materials, compositions, and/or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues, organs, and/or bodily fluids of human beings and animals without excessive toxicity, irritation, allergic response, or other problems or complications commensurate with a reasonable benefit/risk ratio.
"Prevention" or "preventing" includes: (1) inhibiting the onset of a disease in a subject or patient which may be at risk and/or predisposed to the disease but does not yet experience or display any or all of the pathology or symptomatology of the disease, and/or (2) slowing the onset of the pathology or symptomatology of a disease in a subject or patient which may be at risk and/or predisposed to the disease but does not yet experience or display any or all of the pathology or symptomatology of the disease.
"Prodrug" means a compound that is convertible in vivo metabolically into an inhibitor according to the present invention. The prodrug itself may or may not also have activity with respect to a given target protein. For example, a compound comprising a hydroxy group may be administered as an ester that is converted by hydrolysis in vivo to the hydroxy compound. Suitable esters that may be converted in vivo into hydroxy compounds include acetates, citrates, lactates, phosphates, tartrates, malonates, oxalates, salicylates, propionates, succinates, fumarates, maleates, methylene-bis-β-hydroxynaphthoate, gentisates, isethionates, di-p-toluoyltartrates, methanesulfonates, ethanesulfonates, benzenesulfonates, p-toluenesulfonates, cyclohexylsulfamates, quinates, esters of amino acids, and the like. Similarly, a compound comprising an gamine group may be administered as an amide that is converted by hydrolysis in vivo to the amine compound.
A "stereoisomer" or "optical isomer" is an isomer of a given compound in which the same atoms are bonded to the same other atoms, but where the configuration of those atoms in three dimensions differs. "Enantiomers" are stereoisomers of a given compound that are mirror images of each other, like left and right hands. "diastereomers" are stereoisomers of a given compound that are not enantiomers. Chiral molecules contain a chiral center, also referred to as a stereocenter or stereogenic center, which is any point, though not necessarily an atom, in a molecule bearing groups such that an interchanging of any two groups leads to a stereoisomer. In organic compounds, the chiral center is typically a carbon, phosphorus or sulfur atom, though it is also possible for other atoms to be stereocenters in organic and inorganic compounds. A molecule can have multiple stereocenters, giving it many stereoisomers. In compounds whose stereoisomerism is due to tetrahedral stereogenic centers (e.g., tetrahedral carbon), the total number of hypothetically possible stereoisomers will not exceed 2n, where n is the number of tetrahedral stereocenters. Molecules with symmetry frequently have fewer than the maximum possible number of stereoisomers. A 50:50 mixture of enantiomers is referred to as a racemic mixture. Alternatively, a mixture of enantiomers can be enantiomerically enriched so that one enantiomer is present in an amount greater than 50%. Typically, enantiomers and/or diasteromers can be resolved or separated using techniques known in the art. It is contemplated that that for any stereocenter or axis of chirality for which stereochemistry has not been defined, that stereocenter or axis of chirality can be present in its R form, S form, or as a mixture of the R and S forms, including racemic and non-racemic mixtures. As used herein, the phrase "substantially free from other stereoisomers" means that the composition contains ≤ 15%, more preferably ≤ 10%, even more preferably ≤ 5%, or most preferably ≤ 1% of another stereoisomer(s).
"Effective amount," "Therapeutically effective amount" or "pharmaceutically effective amount" means that amount which, when administered to a subject or patient for treating a disease, is sufficient to effect such treatment for the disease.
"Treatment" or "treating" includes (1) inhibiting a disease in a subject or patient experiencing or displaying the pathology or symptomatology of the disease (e.g., arresting further development of the pathology and/or symptomatology), (2) ameliorating a disease in a subject or patient that is experiencing or displaying the pathology or symptomatology of the disease (e.g., reversing the pathology and/or symptomatology), and/or (3) effecting any measurable decrease in a disease in a subject or patient that is experiencing or displaying the pathology or symptomatology of the disease.
As used herein, the term "water soluble" means that the compound dissolves in water at least to the extent of 0.010 mole/liter or is classified as soluble according to literature precedence.
The above definitions supersede any conflicting definition in any of the reference cited herein. The fact that certain terms are defined, however, should not be considered as indicative that any term that is undefined is indefinite. Rather, all terms used are believed to describe the invention in terms such that one of ordinary skill can appreciate the scope and practice the present invention.
Certain embodiments provide compounds that block potassium channels having the following formula:
In some embodiments, the compounds have the formulas found in
In further embodiments, 4-AP derivatives having the following formula are provided:
wherein M is (CH2)nY, and wherein n= 0, 1, or 2, and Y is fluorine or an isotope thereof.
In certain embodiments, there are provided compounds of formula (III):
Further embodiments are directed to the compounds of formula (IV):
The compounds provided by the present disclosure are described in the summary of the invention section and in the claims below.
Compounds employed in methods described herein may contain one or more asymmetrically-substituted carbon or nitrogen atoms, and may be isolated in optically active or racemic form. Thus, all chiral, diastereomeric, racemic form, epimeric form, and all geometric isomeric forms of a structure are intended, unless the specific stereochemistry or isomeric form is specifically indicated. Compounds may occur as racemates and racemic mixtures, single enantiomers, diastereomeric mixtures and individual diastereomers. In some embodiments, a single diastereomer is obtained. The compounds can be formulated as a mixture of one or more diastereomers. Alternatively, the diastereomers can be separated and one or more of the diastereomers can be formulated individually. The chiral centers of the compounds disclosed herein can have the S or the R configuration, as defined by the IUPAC 1974 Recommendations. For example, mixtures of stereoisomers may be separated using techniques known to those of skill in the art.
Atoms making up the compounds of the present invention are intended to include all isotopic forms of such atoms. Compounds of the present invention include those with one or more atoms that have been isotopically modified or enriched, in particular those with pharmaceutically acceptable isotopes or those useful for pharmaceutical research. Isotopes, as used herein, include those atoms having the same atomic number but different mass numbers. By way of general example and without limitation, isotopes of hydrogen include deuterium and tritium, and isotopes of carbon include 11C, 13C and 14C. Similarly, it is contemplated that one or more carbon atom(s) of a compound of the present invention may be replaced by a silicon atom(s). Furthermore, it is contemplated that one or more oxygen atom(s) of a compound of the present invention may be replaced by a sulfur or selenium atom(s).
Compounds disclosed herein may also exist in prodrug form. Since prodrugs are known to enhance numerous desirable qualities of pharmaceuticals (e.g., solubility, bioavailability, manufacturing, etc.), the compounds employed in some methods of the invention may, if desired, be delivered in prodrug form. Thus, certain embodiments contemplate prodrugs of compounds described herein as well as methods of delivering prodrugs. Prodrugs of the compounds may be prepared by modifying functional groups present in the compound in such a way that the modifications are cleaved, either in routine manipulation or in vivo, to the parent compound. Accordingly, prodrugs include, for example, compounds described herein in which a hydroxy, amino, or carboxy group is bonded to any group that, when the prodrug is administered to a subject, cleaves to form a hydroxy, amino, or carboxylic acid, respectively.
It should be recognized that the particular anion or cation forming a part of any salt of this invention is not critical, so long as the salt, as a whole, is pharmacologically acceptable. Additional examples of pharmaceutically acceptable salts and their methods of preparation and use are presented in Handbook of Pharmaceutical Salts: Properties, and Use (2002).
It should be further recognized that the compounds of the present invention include those that have been further modified to comprise substituents that are convertible to hydrogen in vivo. This includes those groups that may be convertible to a hydrogen atom by enzymological or chemical means including, but not limited to, hydrolysis and hydrogenolysis. Examples include hydrolyzable groups, such as acyl groups, groups having an oxycarbonyl group, amino acid residues, peptide residues, o-nitrophenylsulfenyl, trimethylsilyl, tetrahydropyranyl, diphenylphosphinyl, and the like. Examples of acyl groups include formyl, acetyl, trifluoroacetyl, and the like. Examples of groups having an oxycarbonyl group include ethoxycarbonyl, tert-butoxycarbonyl (-C(O)OC(CH3)3), benzyloxycarbonyl, p-methoxybenzyloxycarbonyl, vinyloxycarbonyl, β-(p-toluenesulfonyl)ethoxycarbonyl, and the like. Suitable amino acid residues include, but are not limited to, residues ofGly (glycine), Ala (alanine), Arg (arginine), Asn (asparagine), Asp (aspartic acid), Cys (cysteine), Glu (glutamic acid), His (histidine), Ile (isoleucine), Leu (leucine), Lys (lysine), Met (methionine), Phe (phenylalanine), Pro (proline), Ser (serine), Thr (threonine), Trp (tryptophan), Tyr (tyrosine), Val (valine), Nva (norvaline), Hse (homoserine), 4-Hyp (4-hydroxyproline), 5-Hyl (5-hydroxylysine), Orn (ornithine) and β-Ala. Examples of suitable amino acid residues also include amino acid residues that are protected with a protecting group. Examples of suitable protecting groups include those typically employed in peptide synthesis, including acyl groups (such as formyl and acetyl), arylmethoxycarbonyl groups (such as benzyloxycarbonyl and p-nitrobenzyloxycarbonyl), tert-butoxycarbonyl groups (-C(O)OC(CH3)3), and the like. Suitable peptide residues include peptide residues comprising two to five amino acid residues. The residues of these amino acids or peptides can be present in stereochemical configurations of the D-form, the L-form or mixtures thereof. In addition, the amino acid or peptide residue may have an asymmetric carbon atom. Examples of suitable amino acid residues having an asymmetric carbon atom include residues of Ala, Leu, Phe, Trp, Nva, Val, Met, Ser, Lys, Thr and Tyr. Peptide residues having an asymmetric carbon atom include peptide residues having one or more constituent amino acid residues having an asymmetric carbon atom. Examples of suitable amino acid protecting groups include those typically employed in peptide synthesis, including acyl groups (such as formyl and acetyl), arylmethoxycarbonyl groups (such as benzyloxycarbonyl and p-nitrobenzyloxycarbonyl), tert-butoxycarbonyl groups (-C(O)OC(CH3)3), and the like. Other examples of substituents "convertible to hydrogen in vivo" include reductively eliminable hydrogenolyzable groups. Examples of suitable reductively eliminable hydrogenolyzable groups include, but are not limited to, arylsulfonyl groups (such as o-toluenesulfonyl); methyl groups substituted with phenyl or benzyloxy (such as benzyl, trityl and benzyloxymethyl); arylmethoxycarbonyl groups (such as benzyloxycarbonyl and o-methoxy-benzyloxycarbonyl); and haloethoxycarbonyl groups (such as β,β,β-trichloroethoxycarbonyl and β-iodoethoxycarbonyl).
The compounds described herein may exist in unsolvated forms as well as solvated forms, including hydrated forms. In general, the solvated forms are equivalent to unsolvated forms and are within the scope of the compounds described herein. The compounds described herein may exist in multiple crystalline or amorphous forms. In general, all physical forms are equivalent for the uses described herein and are intended to be within the scope of the compounds described herein.
Compounds provided herein may also have the advantage that they may be more efficacious than, be less toxic than, be longer acting than, be more potent than, produce fewer side effects than, be more easily absorbed than, and/or have a better pharmacokinetic profile (e.g., higher oral bioavailability and/or lower clearance) than, and/or have other useful pharmacological, physical, or chemical properties over, compounds known in the prior art, whether for use in the indications stated herein or otherwise.
The compounds described herein can be formulated for enteral, parenteral, topical, or pulmonary administration. In other embodiments, the formulation is for administration to a subject, but it may not be directly to the subject. The compounds can be combined with one or more pharmaceutically acceptable carriers and/or excipients that are considered safe and effective and may be administered to an individual without causing undesirable biological side effects or unwanted interactions. The carrier is all components present in the pharmaceutical formulation other than the active ingredient or ingredients.
The compounds described herein can be formulated for parenteral administration. "Parenteral administration", as used herein, means administration by any method other than through the digestive tract or non-invasive topical or regional routes. For example, parenteral administration may include administration to a patient intravenously, intradermally, intraarterially, intraperitoneally, intralesionally, intracranially, intraarticularly, intraprostatically, intrapleurally, intratracheally, intravitreally, intratumorally, intramuscularly, subcutaneously, subconjunctivally, intravesicularly, intrapericardially, intraumbilically, by injection, and by infusion.
Parenteral formulations can be prepared as aqueous compositions using techniques is known in the art. Typically, such compositions can be prepared as injectable formulations, for example, solutions or suspensions; solid forms suitable for using to prepare solutions or suspensions upon the addition of a reconstitution medium prior to injection; emulsions, such as water-in-oil (w/o) emulsions, oil-in-water (o/w) emulsions, and microemulsions thereof, liposomes, or emulsomes.
The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, one or more polyols (e.g., glycerol, propylene glycol, and liquid polyethylene glycol), oils, such as vegetable oils (e.g., peanut oil, corn oil, sesame oil, etc.), and combinations thereof. The proper fluidity can be maintained, for example, by the use of a coating, such as lecithin, by the maintenance of the required particle size in the case of dispersion and/or by the use of surfactants. In many cases, it will be preferable to include isotonic agents, for example, sugars or sodium chloride.
Solutions and dispersions of the active compounds as the free acid or base or pharmacologically acceptable salts thereof can be prepared in water or another solvent or dispersing medium suitably mixed with one or more pharmaceutically acceptable excipients including, but not limited to, surfactants, dispersants, emulsifiers, pH modifying agents, and combination thereof.
Suitable surfactants may be anionic, cationic, amphoteric or nonionic surface active agents. Suitable anionic surfactants include, but are not limited to, those containing carboxylate, sulfonate and sulfate ions. Examples of anionic surfactants include sodium, potassium, ammonium of long chain alkyl sulfonates and alkyl aryl sulfonates such as sodium dodecylbenzene sulfonate; dialkyl sodium sulfosuccinates, such as sodium dodecylbenzene sulfonate; dialkyl sodium sulfosuccinates, such as sodium bis-(2-ethylthioxyl)-sulfosuccinate; and alkyl sulfates such as sodium lauryl sulfate. Cationic surfactants include, but are not limited to, quaternary ammonium compounds such as benzalkonium chloride, benzethonium chloride, cetrimonium bromide, stearyl dimethylbenzyl ammonium chloride, polyoxyethylene and coconut amine. Examples of nonionic surfactants include ethylene glycol monostearate, propylene glycol myristate, glyceryl monostearate, glyceryl stearate, polyglyceryl-4-oleate, sorbitan acylate, sucrose acylate, PEG-150 laureate, PEG-400 monolaurate, polyoxyethylene monolaurate, polysorbates, polyoxyethylene octylphenylether, PEG-1000 cetyl ether, polyoxyethylene tridecyl ether, polypropylene glycol butyl ether, Poloxamer® 401, stearoyl monoisopropanolamide, and polyoxyethylene hydrogenated tallow amide. Examples of amphoteric surfactants include sodium N-dodecyl-.beta.-alanine, sodium N-lauryl-.beta.-iminodipropionate, myristoamphoacetate, lauryl betaine and lauryl sulfobetaine.
The formulation can contain a preservative to prevent the growth of microorganisms. Suitable preservatives include, but are not limited to, parabens, chlorobutanol, phenol, sorbic acid, and thimerosal. The formulation may also contain an antioxidant to prevent degradation of the active agent(s).
The formulation is typically buffered to a pH of 3-8 for parenteral administration upon reconstitution. Suitable buffers include, but are not limited to, phosphate buffers, acetate buffers, and citrate buffers.
Water soluble polymers are often used in formulations for parenteral administration. Suitable water-soluble polymers include, but are not limited to, polyvinylpyrrolidone, dextran, carboxymethylcellulose, and polyethylene glycol.
Sterile injectable solutions can be prepared by incorporating the active compounds in the required amount in the appropriate solvent or dispersion medium with one or more of the excipients listed above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those listed above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum-drying and freeze-drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof. The powders can be prepared in such a manner that the particles are porous in nature, which can increase dissolution of the particles. Methods for making porous particles are well known in the art.
Formulations may be stable over a period of 6 months when stored at room temperature or 4°C.
Suitable oral dosage forms include tablets, capsules, solutions, suspensions, syrups, and lozenges. Tablets can be made using compression or molding techniques well known in the art. Gelatin or non-gelatin capsules can prepared as hard or soft capsule shells, which can encapsulate liquid, solid, and semi-solid fill materials, using techniques well known in the art.
Formulations may be prepared using a pharmaceutically acceptable carrier. As generally used herein ''carrier'' includes, but is not limited to, diluents, preservatives, binders, lubricants, disintegrators, swelling agents, fillers, stabilizers, and combinations thereof.
Carrier also includes all components of the coating composition which may include plasticizers, pigments, colorants, stabilizing agents, and glidants. Delayed release dosage formulations may be prepared as described in standard references such as "
Examples of suitable coating materials include, but are not limited to, cellulose polymers such as cellulose acetate phthalate, hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose phthalate and hydroxypropyl methylcellulose acetate succinate; polyvinyl acetate phthalate, acrylic acid polymers and copolymers, and methacrylic resins that are commercially available under the trade name EUDRAGIT® (Roth Pharma, Westerstadt, Germany), zein, shellac, and polysaccharides.
Additionally, the coating material may contain conventional carriers such as plasticizers, pigments, colorants, glidants, stabilization agents, pore formers and surfactants.
Optional pharmaceutically acceptable excipients include, but are not limited to, diluents, binders, lubricants, disintegrants, colorants, stabilizers, and surfactants. Diluents, also referred to as "fillers," are typically necessary to increase the bulk of a solid dosage form so that a practical size is provided for compression of tablets or formation of beads and granules. Suitable diluents include, but are not limited to, dicalcium phosphate dihydrate, calcium sulfate, lactose, sucrose, mannitol, sorbitol, cellulose, microcrystalline cellulose, kaolin, sodium chloride, dry starch, hydrolyzed starches, pregelatinized starch, silicone dioxide, titanium oxide, magnesium aluminum silicate and powdered sugar.
Binders are used to impart cohesive qualities to a solid dosage formulation, and thus ensure that a tablet or bead or granule remains intact after the formation of the dosage forms. Suitable binder materials include, but are not limited to, starch, pregelatinized starch, gelatin, sugars (including sucrose, glucose, dextrose, lactose and sorbitol), polyethylene glycol, waxes, natural and synthetic gums such as acacia, tragacanth, sodium alginate, cellulose, including hydroxypropylmethylcellulose, hydroxypropylcellulose, ethylcellulose, and veegum, and synthetic polymers such as acrylic acid and methacrylic acid copolymers, methacrylic acid copolymers, methyl methacrylate copolymers, aminoalkyl methacrylate copolymers, polyacrylic acid/polymethacrylic acid and polyvinylpyrrolidone.
Lubricants are used to facilitate tablet manufacture. Examples of suitable lubricants include, but are not limited to, magnesium stearate, calcium stearate, stearic acid, glycerol behenate, polyethylene glycol, talc, and mineral oil.
Disintegrants are used to facilitate dosage form disintegration or "breakup" after administration, and generally include, but are not limited to, starch, sodium starch glycolate, sodium carboxymethyl starch, sodium carboxymethylcellulose, hydroxypropyl cellulose, pregelatinized starch, clays, cellulose, alginine, gums or cross linked polymers, such as cross-linked PVP (Polyplasdone® XL from GAF Chemical Corp).
Stabilizers are used to inhibit or retard drug decomposition reactions which include, by way of example, oxidative reactions. Suitable stabilizers include, but are not limited to, antioxidants, butylated hydroxytoluene (BHT); ascorbic acid, its salts and esters; Vitamin E, tocopherol and its salts; sulfites such as sodium metabisulphite; cysteine and its derivatives; citric acid; propyl gallate, and butylated hydroxyanisole (BHA).
Oral dosage forms, such as capsules, tablets, solutions, and suspensions, can for formulated for controlled release. For example, the one or more 4-AP derivatives and optional one or more additional active agents can be formulated into nanoparticles, microparticles, and combinations thereof, and encapsulated in a soft or hard gelatin or non-gelatin capsule or dispersed in a dispersing medium to form an oral suspension or syrup. The particles can be formed of the drug and a controlled release polymer or matrix. Alternatively, the drug particles can be coated with one or more controlled release coatings prior to incorporation in to the finished dosage form.
In another embodiment, the one or more 4-AP derivatives and optional one or more additional active agents are dispersed in a matrix material, which gels or emulsifies upon contact with an aqueous medium, such as physiological fluids. In the case of gels, the matrix swells entrapping the active agents, which are released slowly over time by diffusion and/or degradation of the matrix material. Such matrices can be formulated as tablets or as fill materials for hard and soft capsules.
In still another embodiment, the one or more 4-AP derivatives, and optional one or more additional active agents are formulated into a sold oral dosage form, such as a tablet or capsule, and the solid dosage form is coated with one or more controlled release coatings, such as a delayed release coatings or extended release coatings. The coating or coatings may also contain the 4-AP derivatives and/or additional active agents.
Suitable dosage forms for topical administration include creams, ointments, salves, sprays, gels, lotions, emulsions, and transdermal patches. The formulation may be formulated for transmucosal, transepithelial, transendothelial, or transdermal administration. The compounds can also be formulated for intranasal delivery, pulmonary delivery, or inhalation. The compositions may further contain one or more chemical penetration enhancers, membrane permeability agents, membrane transport agents, emollients, surfactants, stabilizers, and combination thereof.
Any of the formulations discussed above may be used for a formulation that is not a pharmaceutical formulation. In some embodiments, a formulation may be prepared for administration to a subject by a method that is direct or by a method that is indirect. In certain embodiments, a compound is provided in a liquid, solid, or powder formulation. The compound may be in a composition that is sprayed or otherwise applied to a surface or location. In some embodiments, the composition is placed in a location that is accessible to the subject so that the subject ingests or comes into contact with the composition. In certain embodiments, the compound is absorbed or adsorbed by the subject.
The compounds provided by the present disclosure are described in the summary of the invention section and in the claims below. They may be made using the methods outlined in the summary of the invention section and in the Examples section. These methods can be further modified and optimized using the principles and techniques of organic chemistry as applied by a person skilled in the art. Such principles and techniques are taught, for example, in
The compounds or compositions described herein can also be prepared by any of the applicable techniques of organic synthesis and polymer chemistry. Many such techniques are well known in the art. Many of the known techniques are elaborated in
The compounds described herein can also be used as imaging agents in medical imaging applications. Medical imaging is the technique and process used to create images of the human body (or parts and function thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology). Medical imaging may also be applied to an animal body. Commonly used medical imaging techniques include, but are not limited to, radiography, magnetic resonance imaging (MRI), fiduciary markers, nuclear medicine, photo acoustic imaging, breast thermography, tomography, and ultrasound.
Projection radiograph, also known as x-rays, and fluoroscopy are two forms of radiographic images used in medical imaging; with the latter being useful for catheter guidance. This imaging modality utilizes a wide beam of x rays for image acquisition and is the first imaging technique available in modern medicine.
Magnetic resonance imaging instrument (MRI scanner), or "nuclear magnetic resonance (NMR) imaging" scanner as it was originally known, uses powerful magnets to polarise and excite hydrogen nuclei (single proton) in water molecules in human tissue, producing a detectable signal which is spatially encoded, resulting in images of the body.
Fiduciary markers are used in a wide range of medical imaging applications. Images of the same subject produced with two different imaging systems may be correlated (called image registration) by placing a fiduciary marker in the area imaged by both systems. In this case, a marker which is visible in the images produced by both imaging modalities must be used.
Nuclear medicine encompasses both diagnostic imaging and treatment of disease. Nuclear medicine uses certain properties of isotopes and the energetic particles emitted from radioactive material to diagnose or treat various pathology. This approach is often used in e.g., scintigraphy, SPECT and PET to detect regions of biologic activity that may be associated with disease. Isotopes are often preferentially absorbed by biologically active tissue in the body, and can be used to identify tumors or fracture points in bone. Images are acquired after collimated photons are detected by a crystal that gives off a light signal, which is in turn amplified and converted into count data.
Scintigraphy ("scint") is a form of diagnostic test wherein radioisotopes are taken internally, for example intravenously or orally. Then, gamma cameras capture and form two-dimensional images from the radiation emitted by the radiopharmaceuticals.
SPECT is a 3D tomographic technique that uses gamma camera data from many projections and can be reconstructed in different planes. In SPECT imaging, the patient is injected with a radioisotope, most commonly Thallium 201TI, Technetium 99mTC, Iodine 123I, and Gallium 67Ga.
Positron emission tomography (PET) uses coincidence detection to image functional processes. Short-lived positron emitting isotopes, such as 18F, are incorporated with an organic substance such as glucose, creating F18-fluorodeoxyglucose, which can be used as a marker of metabolic utilisation. Images of activity distribution throughout the body can show rapidly growing tissue, like tumor, metastasis, or infection. PET images can be viewed in comparison to computed tomography scans to determine an anatomic correlate. Modern scanners combine PET with a CT, or even MRI, to optimize the image reconstruction involved with positron imaging. This is performed on the same equipment without physically moving the patient off of the gantry. The resultant hybrid of functional and anatomic imaging information is a useful tool in non-invasive diagnosis and patient management.
Tomography is the method of imaging a single plane, or slice, of an object resulting in a tomogram. There are several forms of tomography, including linear tomography, poly tomography, zonography, orthopantomograph (OPT or OPG), and computed tomography (CT).
Medical ultrasonography uses high frequency broadband sound waves in the megahertz range that are reflected by tissue to varying degrees to produce (up to 3D) images. This is commonly associated with imaging the fetus in pregnant women. Uses of ultrasound are much broader, however. Other important uses include imaging the abdominal organs, heart, breast, muscles, tendons, arteries and veins.
In certain embodiments, the compounds described herein are used for in vivo imaging of the central nervous system. More specifically, the compounds described herein bind to potassium channels, including Kv1 channels. The compounds disclosed herein contain one or more radioisotopes. Exemplary radioisotopes include, but are not limited to, 18F, 11C, 13N, and 15O. It would be within an artisan's ordinary skill to choose appropriate radioisotope suitable for the imaging technique intended to use. In some embodiments, one or more imaging techniques may be combined for imaging purposes. For example, PET may be combined with MRI. In some aspects, PET is used to image demyelination and MRI is used to image inflammation. PET and MRI are complement to each other and can provide valuable information on progression of the MS disease in a patient.
One particular embodiment is directed to radiolabelled 4-AP derivatives that target potassium channels of demyelinated neurons. These radio tracers may be used as in vivo imaging agents for demyelination. In particular embodiments, these radiotracers are suitable for PET imaging technique. In one embodiment, the radiotracers described herein contain 18F.
Since the compounds described herein are capable of blocking potassium channels, such as Kv1 potassium channels located in the axonal membrane, the use of 18F-labeled 4-AP derivatives such as [18F]-3-fluoromethyl-4-aminopyridine, or [18F]-3-fluoro-4-aminopyridine, or other radiotracers described herein allows visualization of demyelinated axons in live animals by proper medical imaging techniques, such as PET. Therefore, the compounds described herein may be used to diagnose a demyelinating disease or assessing the progression of a demyelinating disease by administering the compounds to a subject in need thereof and detecting the compounds in the subject by proper medical imaging technique, such as PET, PET-Time-Activity Curve (TAC), PET-MRI, in particular, PET. In some embodiments, one or more medical imaging techniques disclosed herein may be used to diagnose or evaluate the progression of a disease.
In various aspects, a kit is envisioned containing one or more compounds described herein. The kit may contain one or more sealed containers, such as a vial, containing any of the compounds described herein and/or reagents for preparing any of the compounds described herein. In some embodiments, the kit may also contain a suitable container means, which is a container that will not react with components of the kit, such as an Eppendorf tube, an assay plate, a syringe, a bottle, or a tube. The container may be made from sterilizable materials such as plastic or glass.
The kit may further include instructions that outline the procedural steps for methods of treatment or prevention of disease, and will follow substantially the same procedures as described herein or are known to those of ordinary skill. The instruction information may be in a computer readable media containing machine-readable instructions that, when executed using a computer, cause the display of a real or virtual procedure of delivering a pharmaceutically effective amount of one or more compounds described herein.
The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result within the scope of the claims.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of skill in the art to which the disclosed invention belongs.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein.
4-AP (
Furthermore, since Kv1 channels are upregulated 2-4 fold in demyelinated animals such as shiverer mice and upregulation of Kv1 channels in demyelinated axons suggests greater signal, the inventors expect that the signal proceeding from demyelinated axons will be greater.
A common approach in the design of PET radioactive tracers is to replace a hydrogen (H), hydroxyl (OH) or methyl (CH3) group with fluorine-18 (Ametamey et al., 2008). Fluorine-18 is the preferred radionuclide due to its low positron energy and its longer half-life. The low positron energy gives it greater spatial resolution and its longer half-life facilitates off-site production and distribution.
In an effort to design 4-AP derivatives that maintain activity and are suitable for PET imaging, the inventors began by examining 4-AP derivatives that are known to block K+ channels. 4-AP (
Before radioactive labeling, it is important to test whether these fluorinated derivatives are still able to bind to K+ channels. Non-radioactive 3-fluoro-4-aminopyridine (
In order to confirm that the fluorinated 4-AP derivatives maintain the ability to block K+ channels and select the most suitable compound for imaging studies, the inventors measured inhibition of K+ currents in Shaker channels (Kv1.2) using cut-open oocyte voltage clamp (Stefani and Bezanilla,, 1998) (
Remarkably, 3-fluoro-4-ammopyridine (3F-4AP) has very similar affinity to 4-AP for K+ channels. 3-fluoromethyl-4-aminopyridine (3MeF-4AP) is similar to 3-methanol-4-aminopyridine (3MeOH-4AP) and around 10-fold less potent than 4-AP. 3-fluoroethyl-4-aminopyridine (3EtF-4AP) and 2-fluoro-4-aminopyridine (2F-4AP) are at least a hundred fold-less potent than 4-AP. Based on these results, 3F-4AP and 3-MeF-4AP are the preferred molecules for imaging and therapy.
One advantage of 4-AP, and presumably of its analogs, is that they bind to all channels from the Kv1 family. It is known that neurons express several of these channels (Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv1.6, Kv1.7 and Kv1.8, among which the most important neuronal voltage gated K+ channels are Kv1.1 and Kv1.2) and that these channels can form hererotetramers. However, it is unclear which one or several are responsible for the aberrant efflux of K+ ions from demyelinated axons and thus, a broad-spectrum channel may be beneficial.
A desired property for radioactive tracers is high affinity. It is striking that 4-AP and 3,4-diaminopyridine possess a relatively modest affinity to K+ channels (µM to mM) and yet that they are useful in therapeutics (Murray and Newsom-Davis, 1981; Maddison and Newsom-Davis, 2003;Goodman et al., 2009). It is possible that these molecules have a higher effective affinity in vivo as they bind quasi-irreversibly to the channel. Once bound to the channel these molecules become trapped inside the channel and do not dissociate. Thus, it is expected that despite their modest affinity, the PET markers described herein will display a high signal-to-noise ratio.
It is important to note that even though the in vitro affinity of 4-AP is low (∼250 µM), 4-AP is active at much lower concentrations in vivo (∼0.5 µM). This difference might be because blockage of a small fraction of channels already leads to an effect and because 4-AP binds to the channels when they are open and once the channels close, 4-AP becomes trapped inside, functioning as a non-reversible ligand (Armstrong and Loboda, 2001).
A consequence of excessive K+ channel blockage is the advent of seizures. 4-AP is known to cause seizures in mice at high doses. The inventors tested some 4-AP derivatives described herein and compared them to 4-AP in their ability to cause seizures (Table 1).
The fact that only the molecules that are active by cut-open voltage clamp are able to cause seizures strongly suggests that these molecules are targeting K+ channels receptors in vivo.
In addition, the inventors noticed that Shiverer mice, which harbor a mutation on myelin basic protein and suffer from demyelination of the CNS, appear to be less sensitive to 4-AP induced seizures. Previous studies have shown that Shiverers and other demyelinated mice display an abnormal localization pattern of Kv1 channels and a 2-4 fold increase in expression of Kv1.1 and Kv1.2 channels in axons (Wang et al., 1995). The inventors believe that the higher expression of Kv1 channels in Shiverer mice is the reason for why these animals are less sensitive to 4-AP. It is not known whether Kv1 channels are also upregulated in MS patients, but it is known that Kv1 channels in MS lesions present a similar localization patterns as in demyelinated animals (Coman et al., 2006). Therefore, similar upregulation is anticipated. Accordingly, upregulation of Kv1 channels in MS patient lesions combined with the presumed lower accessibility of 4-AP to Kv1 channels in myelinated axons make Kv1 channels an attractive target for PET imaging.
At high doses, 4-AP causes tremors, muscle spasms and seizures. A summary of the observations is shown in Table 1.
From this experiment it can be seen that 3-F-4-AP and 3-MeF-4-AP have very similar effects as 4-AP in mice. Both of these drugs cause salivation, tremors, jerks, extension of the hind limbs and seizures. 3-F-4-AP has very similar potency to that of 4-AP and acts much faster (onset of seizures at highest dose 10 s vs. 10 min) which is consistent with a faster absorption and a higher permeation of the blood-brain barrier. 3-MeF-4-AP is slightly less potent than 4-AP but remarkably potent considering that in the voltage-clamp and optic nerve experiments it was found to be 6 - 20 times less potent than 4-AP. In contrast, 2-F-4-AP and 3-MeOH-4-AP did not cause any effects at doses up to 20 times higher. The inventors also tested the effect of the drugs given by oral gavage on a small number of animals and found the same effects (data not shown).
Based on the report by Lee et al on the synthesis of fluoroalkyl pyridines with fluorine-18 (Lee et al., 1999), this example depicts a possible synthetic route to generate [18F]-3-fluoromethyl-4-aminopyridine by protecting the amine of 4-aminopyridine-3-methanol with Boc, followed by nucleophilic substitution of the benzyl alcohol with 18F-, and boc deprotection.
A solution of Boc2O (0.20 mol) in CH2Cl2 (100 mL, not anhydrous) is added over 20 min to a stirred suspension of 4-aminopyridine-3-methanol (0.20 mol) in CH2Cl2 (200 mL). The resulting solution is stirred at room temperature for 25 min (TLC) and acidified with 1 M HCl (230 mL, 0.23 mol). The phases are separated, and the aqueous layer is washed with CH2Cl2. The combined organic extracts are dried (MgSO4) and evaporated in vacuum to give compound 2 which is used in the next step without further purification.
18F water is added to the reaction vessel followed by [18F-] K222 (2 mg) in acetonitrile (500 ml), and K2CO3 (0.1 mol dm-3, 50 ml) and dried at 100 °C for 20-30 min. Compound 3 (1 mg) in acetonitrile (1000 mL) is added. The reaction vessel is sealed and heated at 100 °C for 10 min. The reaction mixture is cooled, washed from the reaction vessel with water (1.5 mL) and collected in a vial. 3 mL of CF3COOH are added to the vial and the reaction is heated in a microwave (75W, 140 °C) for 3 min. Subsequently, the reaction mixture is purified by reverse phase HPLC. Finally, the fractions containing the product are diluted to 5 mL in PBS.
The synthesis of compound 8 starting from compound 5 may be performed using the same procedure to Example 4.
This example depicts a possible synthetic route to generate [18F]-3-fluoro-4-aminopyridine by double deprotonation of N-boc protected 4-aminopyridine followed by reaction with [18F]-F2 and Boc deprotection. Other synthesis including using the recently reported Pd-mediated electrophilic synthesis (Lee et al., 2011) may also be applicable for synthesizing [18F]-3-fluoro-4-aminopyridine.
To a solution of 9 (200 mmol) in THF (500 mL) at -78 °C is added t-BuLi (282 mL, 1.7 M, 480 mmol) in pentane over 70 min. The resulting bright yellow suspension is stirred at -78 °C for 20 min and at -15 °C for 2 h. Subsequently, [18F]-F2 is bubbled through 5 ml of solution containing lithiated species 10. After 20 min, 3 mL of CF3COOH are added to the solution and the reaction is heated in a microwave (75W, 140 °C) for 3 min to afford compound 11.
Alternatively, the 18F-labeled versions of 3-F-4-AP and 3-MeF-4-AP are synthesized as depicted below based on the synthesis of similar PET markers (
The proposed synthesis of [18F] 3-F-4-AP uses iodonium salts for high efficiency synthesis of aryl fluorides. (Chun, et al., 2012). This tracer may be useful to evaluate lesion size and lesion load in multiple sclerosis patients. This tracer may also be useful in patients with Parkinson's disease, stroke, Cerebral palsy, Alzheimer disease, ALS, Lambert Eaton, brain tumors and other diseases.
Synthesis of [18F] 3-F-4-AP (13): Koser reagent is added to a solution of 4-[(tert-butoxycarbonyl)amino]pyridin-3-ylboronic acid (10) in CH2Cl2 and stirred until formation of {4-[(tert-butoxycarbonyl)amino]pyridin-3-yl}(phenyl)iodonium (11). After 16 h the solvent is removed under vacuo and the product (11) purified using standard techniques. Next {4-[(tert-butoxycarbonyl)amino]pyridin-3-yl}(phenyl)iodonium (11) is dissolved in DMF and [(crypt-222)K]+ 18F- is added to generate [18F] N-(3-fluoropyridin-4-yl)carbamate (12). Finally, [18F] N-(3-fluoropyridin-4-yl)carbamate (12) is treated with aqueous HCl to deprotect the amino gropu and yield the final product [18F] 3-fluoropyridin-4-amine also known as [18F] 3-fluoro-4-aminopyridinine or [18F] 3-F-4-AP
Once the radiolabeled markers are obtained, the inventors will perform imaging studies in several mouse models of demyelination. The compounds are tested for imaging demyelination as previously described (Stankoff et al., 2011). The use of different mouse models will enable the inventors to assess whether 4-AP mainly targets potassium channels in neurons or also channels in other cells such as lymphocytes. Suitable animal models, in particular, mouse models, are contemplated as follows.
DTA Model. The inventors have generated a new mouse model (DTA) of widespread CNS demyelination wherein the ablation of oligodendrocytes is accomplished via cell-specific activation of diphtheria toxin (DT-A) expression in young adult animals (Traka et al., 2010). This approach results in widespread DT-A-mediated death of mature oligodendrocytes and extensive demyelination throughout the CNS (Traka et al., 2010). At the peak of disease the DTA mice developed severe tremor and ataxia. These mice demonstrate a gradual recovery that culminates in full attenuation of the disease symptoms by approximately 70 dpi, which correlates with the repopulation of oligodendrocytes and remyelination. This model provides widespread and extensive demyelination of the CNS.
Cuprizone-induced demyelination. Feeding of cuprizone (bis-cyclohexanone oxaldihydrazone) to young adult mice induces a synchronous and consistent demyelination of the corpus callosum (Matsushima and Morel, 2001; Stidworthy et al., 2004). Demyelination and oligodendrocyte apoptosis do not involve T cells or breakdown of the blood-brain barrier in this model and the mice do not display any clinical symptoms. Following the loss of oligodendrocytes and demyelination, there is a depopulation of the oligodendrocytes in the corpus callosum and robust demyelination. The inventors have considerable experience using the cuprizone protocol to examine the demyelination and remyelination processes (Gao et al., 1999; Lin et al., 2004). The cuprizone model provides a nice system in which to image highly reproducible, focal demyelinated lesions that do not involve peripheral immune system infiltration.
Experimental autoimmune encephalomyelitis (EAE). EAE which is considered the best animal model of MS, can be induced in a variety of species of laboratory animals by immunization with either myelin or one of its components (Prog. Clin. Biol. Res., 1984; Zamvil and Steinman, 1990; Martin and McFarland, 1995). EAE is an immune-mediated demyelinating disease that displays many of the clinical, pathologic, and immunological features of MS (Behi et al., 2005). Clinical symptoms correlate with focal inflammatory demyelinated lesions in the spinal cord of the affected animals. The EAE model is capable of providing the most MS-like lesions, which include loss of oligodendrocytes, demyelination and T cell infiltration.
Other animal models of demyelination, such as a lysolecithin injection model, may also be used in the study of demyelination associated diseases. Animal models other than mouse models may also be used. It will be obvious to those skilled in the art to choose an appropriate animal model to adapt to intended research purposes.
A detectable amount of the compound described herein, such as [18F]-3-fluoromethyl-4-aminopyridine, or [18F]-3-fluoro-4-aminopyridine, is introduced in the patient body via a pharmaceutically acceptable route known in the art. The patient is positioned inside a PET scanner or an instrument capable of detecting radiation emitted by the compound as typically done in the art. The localization of the radioactive tracer is done using a computer, which can provide images of the localization and extent of demyelinated axons.
Non-radioactive Synthesis: Non-radioactive synthesis has been performed using standard techniques in organic chemistry. Reactions were monitored by TLC and products characterized by 1H, 13C and 19F NMR, and high-resolution mass spectroscopy.
All chemicals were ordered from Sigma unless otherwise specified. Animal protocols were approved by IACUC.
Synthesis of tert-butyl N-[3-(hydroxymethyl)pyridin-4-yl]carbamate (8): To a solution of 4-aminopyridine-3-methanol (3) (Alfa Aesar) (806 mg, 6.5 mmol) in CH2Cl2 (10 mL) a solution of di-tert-butyl-dicarbonate (1.43 g, 6.56 mmol) in CH2Cl2 (5 mL) was added and stirred at room temperature for 1 h (TLC). After 1 h, the solution was acidified with 1 N HCl (7.4 mL, 7.4 mmol). The phases were separated and the aqueous phase was washed with CH2Cl2. The aqueous layer was mixed with a fresh portion of CH2Cl2 (10 mL) and treated with K2CO3 (711 mg, 5.1 mmol). The phases were separated and treated with additional amounts of CH2Cl2. The combined organic extracts were dried (MgSO4) and evaporated in vacuo to give a 60:40 mixture containing desired product 8 and the O-linked carbonate. Attempts to purify the N-carbamate by flash chromatography from the O-carbonate were unsuccessful due interconversion between these two species in solution at room temperature. 1H-NMR (CDCl3, 500 MHz) δ: 1.53 (9H, s), 4.67 (2H, s), 4.83 (2H, br s), 7.95 (1H, s), 8.07 (1H, d, J= 5.5 Hz), 8.28 (1H, d, J= 5.5 Hz), 8.48 (1 H, s). This product has been previously synthesized through a different route (Mochizuki, et al., 2011).
Synthesis of tert-butyl N-[3-(fluoromethyl)pyridin-4-yl]carbamate (9): To a solution of triethylamine (450 µL, 2.76 mmol) in CH2Cl2 (5 mL) at - 78 °C was added XtalFluor-E® (473 mg, 207 mmol) and the product from the previous reaction (310 mg, 1.38 mmol in 5 mL CH2Cl2). The reaction was stirred at 0 °C for 15 min (TLC). Subsequently, the reaction mixture was washed with NaHCO3 (10 mL) and brine (10 mL). The organic phase was dried (MgSO4) and concentrated in vacuo. The crude product was purified by flash chromatography to afford 9 (113 mg, 36 % yield). Rf = 0.5 (1:1, hexanes: EtOAc). 1H-NMR (CDCl3, 500 MHz) δ ppm: 1.56 (9H, s), 5.48 (2H, d, J = 48 Hz), 7.12 (1H, br s), 8.12 (1H, d, J = 5.5 Hz), 8.38 (1H, d, J = 3 Hz), 8.32 (1H, s), 8.53 (1H, dd, J2 = 5.5 Hz, J1 = 1.0 Hz). 13C-NMR (CDCl3, 125 MHz) δ: 28.2, 80.6, 82.0 (d, J = 15.5 Hz), 113.2, 118.0 (d, J = 15.5 Hz), 145.6, 150.1, 149.7, 151.7, 152.4. 19F-NMR (CDCl3, 470 MHz) δ: -209.3 (t, J = 48 Hz). HR-MS m/z: 227.1190 (M+H)+.
Synthesis of 3-fluoromethyl-4-aminopyridine (5): To a solution of 9 (56 mg, 0.25 mmol) in CH2Cl2 (3 mL) was added TFA (194 µL, 2.5 mmol) at 0 °C and stirred at room temperature for 5 h (TLC). After 5 h the reaction was quenched with excess NaOH (1 M). The solvent was evaporated to afford 8 quantitatively. Rf= 0.2 (MeOH). 1H-NMR (500 MHz, D2O) δ: 5.40 (2H, d, J = 48 Hz), 6.87 (1H, d, J = 7 Hz), 7.95 (1H, d, J = 7 Hz), 8.09 (1H, s). 19F-NMR (CDCl3, 470 MHz) δ: -215.9 (t, J = 48 Hz). HR-MS m/z: 127.0666 (M+H)+.
Synthesis of tert-butyl N-[3-(2-hydroxyethyl)pyridin-4-yl]carbamate (11): Adapted from Spivey et al: To a solution of 4-(Boc-amino)pyridine (1) (2.0 g, 10.3 mmol, 1 eq.) in 25 mL of dry THF at -78 °C was added t-BuLi (14.5 mL, 1.7 M, 24.7 mmol, 2.4 eq.) in pentane over 30 min. The resulting bright yellow suspension was stirred at -78 °C for 15 min, at -15 °C for 2h and then recooled to -78 °C. In a separate flask, n-BuLi (7.38 mL, 2.5M, 18.54 mmol, 1.8 eq) in hexanes was added to a solution of 2-bromoethanol (1.294 mL, 15.45 mmol, 1.5 eq) in 20 mL of dry THF at -78 °C and stirred for 10 min. After 10 min, the bromoethanol solution was transferred via cannula to the flask containing lithiated N-boc-4-aminopyridine over 10 min. The reaction was allowed to warm to room temperature and the mixture was stirred for 2h. The reaction was recooled to -78 °C and quenched with 5 mL of water. The solution was partitioned between water (20 mL) and CH2Cl2 (30 mL). The phases were separated and the extraction was completed with additional portions of CH2Cl2. The combined organic extracts were washed with brine, dried over MgSO4 and evaporated under vacuum. The crude product was dissolved in a small amount of CH2Cl2 purified by silica gel chromatography (EtOAc) to afford the product 11 (0.678 g, 36% yield). Rf = 0.15 (EtOAc). 1H-NMR (500 MHz, CDCl3) δ: 1.51 (9H, s), 2.81 (2H, t, J = 5.0 Hz), 3.80 (1H, br s), 3.94 (2H, t, J = 5.0 Hz), 7.92 (1H, d, J = 5.5 Hz), 8.15 (1H, s), 8.27 (1H, d, J = 5.5 Hz), 8.63 (1H, s).
Synthesis of tert-butyl N-[3-(2-fluoroethyl)pyridin-4-yl]carbamate (12): To a solution of Et3N-3HF (715 µL, 4.39 mmol, 2 eq.) in 5 mL of dry CH2Cl2 at 0 °C, XtalFluor E® (753 mg, 3.29 mmol, 1.5 eq) was added and stirred for 5 min. After 5 min, 2 (525 mg, 2.195 mmol, 1 eq) was added and the reaction was monitored by TLC (1:1, hexanes:EtOAc). 15 min later the reaction was washed with NaHCO3 (5 mL) and brine (5 mL), dried with MgSO4 and the solvent evaporated under vacuum. The crude product was dissolved in a small amount of CH2Cl2 and purified by silica gel chromatography to afford 3 (457 mg, 71 % yield). Rf = 0.4 (1:1, hexanes:EtOAc). Mp = 103 °C. 1H-NMR (500 MHz, CDCl3) δ: 1.53 (9H, s), 2.98 (2H, dt, J2 = 29 Hz, J1 = 5.8 Hz), 4.72 (2H, dt, J2 = 47 Hz, J1 = 5.8 Hz,), 7.04 (1H, d, J = 7.5 Hz), 7.99 (1H, d, J = 5.0 Hz), 8.32 (1H, s), 8.40 (1H, d, J = 5.0 Hz). 13C-NMR (CDCl3, 125 MHz) δ: 28.2, 30.4 (d, J = 20.1 Hz), 81.6, 84.9 (d, J = 165 Hz), 113.7, 121.0, 144.7, 149.7, 151.2. 19F-NMR (CDCl3, 470 MHz) δ: -213.3 (tt, J2 = 47 Hz, J1 = 29 Hz). HR-MS m/z: 241.1347 (M+H)+.
Synthesis of 3-fluoroethyl-4-aminopyridine (6): To a solution of 12 (120 mg, 0.5 mmol, 1 eq.) in 5 mL of CH2Cl2 was added TFA (191 µL, 2.5 mmol, 5 eq) at 0 °C. The reaction was allowed to warm up to room temperature and stirred for 5 h (TLC). After 5 h, the reaction was quenched with excess NaOH (1 M) and extracted multiple times with CH2Cl2. The solvent was evaporated to afford 4 quantitatively. Rf = 0.5 (MeOH). 1H-NMR (500 MHz, CDCl3) δ: 2.91 (2H, dt, J2 = 26.5 Hz, J1 = 6 Hz), 4.26 (2H, br s), 4.69 (2H, dt, J2 = 47 Hz, J1 = 6 Hz), 6.54 (1H, d, J = 5.5 Hz), 8.13 (1H, s), 8.15 (1H, d, J = 5.5 Hz). 13C-NMR (CDCl3, 125 MHz) δ: 30.2 (d, J = 20.6 Hz), 84.2 (d, J = 166 Hz), 110.1, 149.1, 151.0, 151.7. 19F-NMR (CDCl3, 470 MHz) -213.3 (tt, J2 = 47 Hz, J1 = 26.5 Hz). HR-MS m/z: 141.0823 (M+H)+.
[18F] labeling (prophetic): 18F-labeling will be performed using cyclotron-generated reagents for nucleophilic and electrophilic fluorination.
Measure Compound Action Potential of demyelinated nerves: 4-AP can enhance the Compound Action Potential in demyelinated nerves. The effects of the 4-AP derivatives in the compound action potential of optic nerves and/or spinal cords from demyelinated animals will be measured according the protocol by Stys et al. Briefly, optic nerves will be removed postmortem and placed in an oxygenated aCSF solution. Suction electrodes will be used to measure CAP in the presence and absence of the test compounds (Stys et al., 1991).
Imaging (prophetic): Six mice of each group (DT-A, Cuprizone, EAE and healthy controls) will be used for the Imaging study. 100 µCi/100 µL of [18F]-labeled 4-AP derivative will be injected into the tail vein of anesthesized mice. The imaging sessions will be carried out as 1 h dynamic scan using the MicroPET scanner. The MicroPET data will be processed using filter back projection algorithm with attenuation and scatter corrections. In vitro stability studies of the radioactive tracers will be performed according to the protocol by Zhou et al. (2009). Briefly, 2 mL of heparinized mouse blood (C57BL/6N mice) are incubated with the radioactive tracer (∼400 µCi) for 5 min, 30 min, 1h and 2h at 37 °C. At each time point the blood will be lysed with 3 volumes of ethanol and centrifuged. The radioactive species in the supernatant will be analyzed by radio-TLC and compared to the radioactive tracer's control. In vivo stability; ∼400 µCi of [18F] 4-AP in 200 µL of saline are injected into a mouse by iv injection in the tail vein of an immobilized mouse. Blood samples (0.5 mL) are obtained via cardiac puncture under anesthesia at 5 and 30 min post-injection. Afterwards, the plasma is treated with 3 equivalents of acetonitrile and the pellet separated by centrifugation. The radioactivity species of the supernatant will be analyzed by radio-TLC and compared to control. In vivo biodistribution time-course study: ∼400 µCi of [18F] 4-AP in 200 µL of saline will be injected into a mouse by iv injection. At 5 min, 30 min, 1h and 2h post injection the mice will be sacrificed and blood tissues and organs removed, weighed and counted using a Beckman counter with standard diluted aliquots of the sample. The percent injected dose per gram of tissue will be calculated.
Neurological evaluation (prophetic): the effects of the 4-AP derivatives in demyelinated animals will be evaluated using a rotorod to test for balance and coordination, the inventors will also measure changes in tremor and other functions.
Pharmacology of 4-AP derivatives (prophetic): metabolic stability, membrane permeability, toxicity, pharmacokinetic and drug distribution studies will be conducted with the assistance of a third party research contract organization.
Measurement of 4-AP and derivatives distribution in mice (prophetic): The distribution of 4-AP and derivatives will be measure using MALDI-IMS.
The inventors tested the ability of compounds 1-7 to block voltage-gated K+ channels expressed in Xenopus oocytes using the cut-open voltage clamp technique described by Stefani and Bezanilla. For this experiment, Shaker K+ channel from D. megalonaster was chosen as the archetypical voltage gated K+ channel that gives name to the family. Shaker shares an identity ranging from 69%-79% with neuronal Kv1.1, Kv1.2, Kv1.3, Kv1.4, Kv1.6 that are among the presumed targets of 4-AP and its sensitivity to 4-AP is comparable to other Kv1 channels (Gutman, et al., 2005; McCormack, et al., 1994) In order to compare the relative potency of the different 4-AP derivatives, each drug was applied at increasing concentrations and the ratio between the K+ current with and without drug was computed (
Electrophysiology: Electrophysiology studies are conducted according to the protocol by Stefani and Bezanilla (1998). Briefly, K+ channel Shaker cRNA is injected into Xenopus oocytes 24h after their surgical extraction from adult frogs. 1-5 days after injection channel currents are recorded using the cut-open voltage-clamp. Each molecule is added to the external solution at a range of concentrations and K+ currents recorded and compared to those with 4-AP.
Expression of Shaker K+ channel in Xenopus laevis oocytes: K+ channel expression in Xenopus oocytes membranes was achieved by injecting approximately 50 ng of WT Shaker cRNA (kit Ambion) into the oocytes 24 h after surgical extraction from adult frogs and collagenase treatment. Injected oocytes were maintained in a standard oocytes solution (100 mM NaCl, 5 mM KCl, 2 mM CaCl2, and 10 mM Hepes at pH 7.5) at 16.5 °C and recordings were performed 1-3 days after injection.
Recording of K+ currents in Xenopus oocytes: K+ currents were recorded from oocytes expressing Shaker K+ channels using the cut-open voltage clamp technique as described by Stefani and Bezanilla. The internal solution was 120 mM KOH, 20 mM HEPES-methyl sulfonate (MES) pH 7.4, 2 mM EGTA. The external solution was 12 mM KOH, 105 mM N-methyl-D-glucamine-MES pH 7.4, 20 mM HEPES, 2 mM CaOH. To assess the effects of the 4-AP derivatives, the drug under study was added in incremental concentrations by exchanging the external solution (top and guard chambers) several times. After application, cells were voltage-clamped at least 5 min at 0mV, Then voltage-clamped at -80mV for 1-2 min. K+ currents were generated by applying series of 50 ms pulses from -70 mV to +40 mV in increments of 10 mV. The effect of the drug was assessed by measuring the relative intensity of the K+ current before and after applying varying drug concentration at a constant voltage (typically +20 mV) and at the end of the test-pulse. Analysis of the traces was done using an in-house software. The half-maximal inhibitory concentration (IC50) for each drug was calculated by plotting the relative K+ current vs. concentration and fitted to the Hill equation using the software Origin.
In this experiment, it was demonstrated that 4-AP and 3-F-4AP are the most potent compounds with half-maximal inhibitory concentrations (IC50) around 0.27 mM (4-AP: IC50 = 0.29 mM, 95 % C.I. = 0.21 - 0.41 mM; 3-F-4-AP: IC50 = 0.25 mM, 95 % C.I. = 0.13 - 0.44 mM), which is similar to what has been reported for other Shaker-like channels (Gutman, et al., 2005). Although Berger, et al, 1989, described 3-F-4-AP as being less potent than 4-AP in eliciting muscle twitches in dissected mouse hemidiaphragms it was found to have comparable potency in blocking Shaker K+ channel. In this assay, 3-MeOH-4-AP and 3-MeF-4-AP were found to be between 15 and 25 times less potent than 4-AP (3-MeOH-4-AP: IC50 = 4.38 mM, 95 % C.I. = 3.4 - 5.6 mM; 3-MeF-4-AP: IC50 =7.45 mM, 95 % C.I. = 6.2-9.0 mM). In contrast, 3-EtF-4-AP and 2-F-4-AP have IC50 values greater than 10 mM (95% C.I. not determined). These results demonstrate that only small modifications in the 2 position of 4-AP are permitted (e.g. 3-F-4-AP, 3-MeF-4-AP, 3-MeOH-4-AP) whereas larger modifications such as 3-EtF-4-AP or substitution in the 2 position such as 2-F-4-AP significantly diminish activity. In this experiment, it was also observed that these drugs are difficult to wash, out which is similar to what has been reported for 4-AP (McCormack, et al., 1994), suggesting a similar mode of binding.
It is known that 4-AP can significantly enhance action potential of demyelinated fibers (Sherratt, et al., 1980; Devaux, et al., 2002) In order to determine if the drugs could also be effective in enhancing compound action potentials (CAP), the effects of these compounds on the CAP of hypomyelinated optic nerves from Shiverer mice (shi-/-) and control mice (shi+/-, shi+/+) were tested. Shiverer mice lack compact myelin in the CNS due to a null mutation of the myelin basic protein gene (MBP). The results of this experiment are shown in
Dissection of optic nerves from Shiverer mice: optic nerves were dissected from 12-16 week old Shiverer (shi-/-) and control mice (shi+/- and shi+/+). Mice were euthanized by CO2 overdose and the optic nerves were quickly dissected between the eyeball and the optic chiasm. The nerves were incubated for 30 min at 37 °C in oxygenated (95% O2, 5% CO2) aCSF solution (126 mM NaCl, 3 mM KCl, 2 mM MgSO4, 26 mM NaHCO3, 2 mMCaCl2, 10 mM dextrose, pH 7.5) before the experiment.
Optic nerve electrophysiology: compound action potentials (CAP) from hypomyelinated nerves (Shiverer mice, shi-/-) and myelinated nerves (litermate controls, shi+/- and shi+/+) were recorded using suction electrodes as described by Stys et al. Briefly, the dissected optic nerve was placed inside a chamber containing oxygenated (5 % CO2, 95 % O2) aCSF (300 µL) between two suction electrodes (stimulus and recording electrodes) forming a tight seal on each end. Two additional electrodes were placed in the bath for reference. A supramaximal pulse (250 mV, 20 µs) was applied at the stimulating end of the nerve. The resulting CAP was amplified from the recording electrode using a high impedance low-noise amplifier (EG&G Princeton Applied Research Corporation) and filtered and sampled at 10-100 kHz. To assess the effects of the 4-AP derivatives on the CAP, the drug under study was added in incremental concentrations to the recording chamber after the CAP was allowed to stabilize for 5 min while pulsing repeatedly. After each measurement the chamber was washed for 5 min (flow 1 mL/min) with oxygenated aCSF. The study was conducted at 22.2 ± 1.3 °C to allow for slower conduction and the temperature was monitored throughout the experiment. CAP recordings were acquired with a SBC6711 board (Innovative Integration) controlled by in-house written software. Analysis of the traces was done using an in-house software. The half-maximal effective concentration (EC50) for each drug was calculated by plotting the final over initial amplitude vs. concentration and fitted to the Hill equation using Origin.
This experiment shows the typical differences between normally myelinated nerves and hypomyelinated nerves. The Shiverer's hypomyelinated nerves conducted much slower (average conduction velocity 0.59 ± 0.10 m/s vs. 1.4 ± 0.3 m/s at 22 °C), had a smaller CAP amplitude (20-30 % compared to myelinated nerves) and showed a larger undershoot than control nerves. Addition of 4-AP to normally myelinated nerves caused small increases in CAP amplitude of around 5 % and broadening of the signal, whereas addition of 4-AP to hypomyelinated nerves caused large increases in CAP amplitude of 2-4 fold generating a CAP that, although delayed, almost looked like a normally myelinated nerve (
The permeability of 3-F-4-AP and 4-AP to an artificial membrane made of porcine brain polar lipids was tested. In this experiment, the inventors included highly permeable verapamil and lowly permeable theophylline as controls. The inventors found 3-F-4-AP to be 6.6-times more permeable than 4-AP (Pe: 15.6 ± 0.6 nm/s vs. 2.36 ± 0.03 nm/s,
The stability of these drugs in mouse plasma and mouse liver microsomes was also tested. Liver microsomes contain large amounts of cytochrome P450 and can be used to estimate the metabolic stability of drugs. In this experiment, highly stable verapamil and lowly stable propanolol were included as controls. Both drugs were found to be stable in plasma (> 93 % remaining after 1 h) and 3-F-4-AP was found to be 2.7-times more stable than 4-AP in microsomes (4-AP: t1/2 = 53 ± 10 min; 3-F-4-AP: t1/2 = 144 ± 11 min) (
Pharmacokinetic profiling of 4-AP and 3-F-4-AP in mice after a single intravenous dose of the drugs at 0.75 mg/kg (
In vivo effects: 10-week-old female C5781/6J mice were given an intraperitoneal injection of the drug under investigation and monitored continuously for 4 h. After 4 h no signs of drug effects could be observed. At least 72 h passed between injections to the same mice.
Parallel artificial membrane permeability assay (PAMPA): Permeability studies were performed as previously described by Sugano, et al., 2011. A 96-well microplate (acceptor compartment) was filled with PBS containing 5% DMSO. A hydrophobic filter plate (donor compartment) was placed atop the buffer-filled plate and the filter surface was impregnated with 5 µL solution of porcine polar brain lipids (Avanti Lipids) in dodecane (1% w/v). 150 µL of the test compounds dissolved in PBS containing 5% DMSO (compound concentration 0.5 mM) was added to the donor compartment and covered. The only barrier between the two compartments was the artificial BBB membrane containing the porcine polar brain lipids. The whole system was incubated for several hours. Time of incubation was chosen considering cLogP of tested compounds (4 h for Verapamil and 16 h for 4-aminopyridine, 3-fluoro-4-aminopyridine and theophylline). Samples from the acceptor compartment were analyzed by UV-VIS spectrophotometry (4-aminopyridine: 260 nm, 3-fluoro-4-aminopyridine: 265 nm) and compared to reference solutions.
Stability in plasma: Plasma stability was conducted by incubating each compound at initial concentration of 1 µM in mouse plasma for 60 minutes. Samples were collected at 0, 20, 40 and 60 minutes and the reaction was stopped by addition of 1 vol. of acetonitrile. The loss of compound was determined using LC-MS comparing the peak area at several time points. Half-life time was calculated from linear regression of time course data.
Stability in microsomes: study compounds were incubated at initial concentration of 1 µM with liver microsomes from CD1 mouse (0.04 mg/mL) in PBS in the presence or absence of enzyme cofactors (1.3 mM NADP+, 3.3 mM MgCl2, 3.3 mM G6P and 1 U/ml G6PDH, 1 mM UDPGA and 4.7 µg/ml Alamethicin). After t = 0, 20, 40 and 60 min, a sample was removed and the reaction was stopped by adding 1 volume of acetonitrile. The loss of compound was determined by LC-MS analysis comparing the amount of compound in the sample to the respective reference samples (without cofactors). To ensure that the assay is reliable, Propanolol and Verapamil were included as control compounds. The results were normalized for reaction volume and protein concentration.
LC-MS: The following conditions were used for LC-MS analysis. Solvent A: Water (0.1% Formic acid). Solvent B: Acetonitrile (0.1% Formic acid). Flow rate: 0.5 ml/min. Gradient conditions: 0.0 - 0.5 min 95% B, 0.5 - 6.0 min 5% B, 6.0 - 6.5 min 5% B, 6.5 - 6.6 min 95% B, 6.6 - 7.5 min 95% B. Running time: 7.5 min. Injection volume: 40 µl. Column: Luna HILIC, 150 x 4.6 mm, 3 µm. Ionization mode: ESI positive. MS mode: Multiple Reaction Monitoring (MRM). Capillary voltage: 4500 V. Nebuliser gas: 40 psi. Dry gas: 9 L/min. Dry Temperature: 300°C. HPLC and MS/MS parameters: 4-aminopyridine retention time 3.5 min, ion product 94.9. 3-fluoro-4-aminopyridine retention time 4.0 min, ion product = 112.9.
Pharmacokinetic study: 39 mice (CD-1, 6-weeks old, female) were used in the study. 18 mice were administered 4-aminopyridine, 18 mice were administered 3-fluoro-4-aminopyridine and 3 were left untreated. The drugs were dissolved in PBS and administered via tail-vein injection to achieve a dose of 0.75 mg/kg of body weight. At specific times post injection (10 min, 30 min, 1 h, 2 h, 4 h and 24 h) blood and brain samples were collected. Blood samples were transferred into tubes containing 5% EDTA, stored on ice, and centrifuged (4°C, 1000 rpm, 15 min). Plasma (upper phase) was transferred to a new tube and stored at -80°C for further analysis. Brain tissue samples were collected after intracardial perfusion of the mouse. Brain tissue samples were stored at -80°C for further analysis. Drug quantification in plasma: Briefly, to a 1.5 mL Eppendorf tube containing 50 µl of plasma, 200 µl of ice-cold acetonitrile containing 1,000 ng/ml Progesterone (used as internal standard) was added in order to precipitate the proteins. The sample was vortexed, mixed and centrifuged at 4000 x g for 10 min at 4°C to remove precipitates. 140 µl supernatant was collected and transferred to a 500 µl 96-wel polypropylene plate and covered using silicone plate mat. 40 µl of sample was injected in into LC-MS. Using the same sample preparation procedure 11 standard solutions ranging from 50 ng/mL to 100 µg/mL were prepared, analyzed by LC-MS and used as a calibration curve to correlate peak area of the samples to concentration. Drug quantification in brain: the mouse brain was weighted and 1 mL of water per 400 mg of tissue was added. The sample was homogenized using an electric tissue homogenizer. To a 1.5 mL Eppendorf tube containing 50 µl of homogenized sample, 200 µl of ice-cold acetonitrile containing 1000 ng/ml Demeclocycline (used as internal standard) was added in order to precipitate the proteins. The sample was vortexed, mixed and centrifuged at 4000 x g for 10 min at 4°C to remove precipitates. 140 µl supernatant was collected and transferred to a 500 µl 96-well polypropylene plate and covered using silicone plate mat. 40 µl of each sample was injected into LC-MS. Using the same sample preparation procedure 11 standard solutions ranging from 50 ng/mL to 100 µg/mL were prepared, analyzed by LC-MS and used as a calibration curve to correlate peak area of the samples to concentration.
Data analysis: The Hill equation used to fit the data from the voltage-clamp and the optic nerve experiments was as follows: y = y0 + (yf - y0) * xn / (kn + xn); where n refers to the Hill coefficient (typically 1 ± 0.1) and k refers to EC50 or IC50. y0 and yf refers to the origin and final ordinate values and were fixed at 1 ± 0.1 or 0 ± 0.1 depending on the experiment. EC50 = 10<logEC50>; where <logEC50> = average of logEC50 values from all experiments with the same drug. 95% C.I. = [Upper Limit .. Lower Limit]; where U.L. = 10(logEC50 + s.d.) and L.L. = 10(logEC50 - s.d.). The half-life (t1/2) in the stability and pharmacokinetic experiments was calculated by fitting the data to the equation Ct = C0 * exp(-k*t) where C0 = initial concentration, Ct = concentration at time t, and k = ln2/t1/2. Student t-test was used to compare results and P < 0.05 was considered significant.
The inventors conducted an experiment to evaluate if 4-AP selectively localizes in demyelinated areas. In this experiment, tritium labeled 4-aminopyridine ([3H] 4-AP) was injected into mice containing demyelinating lesions in the brain. The lesions were caused by prior injection of lysophosphatidylcholine (LPC), also called lysolecithin, into their brains, which causes focal demyelination at the site of injection. Two days after LPC injection, at the peak of demyelination, the animals were injected with [3H] 4-AP (0.5 mg/kg, 5 µCi/g) via tail vein injection. Thirty to ninety min after injection of [3H] 4-AP the mice were euthanized and their brains were dissected and frozen. The frozen brains were then cut into 20 µm sections using a cryostat and the sections mounted in slides. The slides were then exposed to radiation sensitive X-ray film at -80 °C in the dark for forty days to capture the distribution of radioactivity coming from [3H] 4-AP throughout the brain.
After autoradiographic exposure, the slides were stained for myelin basic protein (MBP) using immunohistochemistry and imaged using fluorescent microscopy to determine the areas of demyelination. The results of this experiment are shown in
This experiment demonstrates that 4-AP selectively localizes to grey matter areas and there's virtually no 4-AP in white matter areas. It was also observed that demyelination of white matter areas causes a local increase in the autoradiographic signal indicating that 4-AP localizes to demyelinated areas but not myelinated areas.
It was shown that fluorinated 4-APs can block Shaker K+ channel similar to 4-AP, that fluorinated 4-APs can enhance compound action potential of dysmyelinated optic nerves but have very little effect on normally myelinated optic nerves, and that fluorinated 4-APs have very similar in vivo effects as 4-AP. It was also shown that fluorinated 4-APs have enhanced permeability to the CNS relative to 4-AP. As 4-AP localizes to demyelinated areas and fluorinated 4-APs have very similar biological activity to 4-AP, it can be inferred that fluorinated 4-APs also localizes to demyelinated lesions. As fluorinated molecules can be used as PET tracers simply by exchanging the natural isotope of fluorine (19F) for the positron emitting isotope 18F and this exchange does not alter the biological properties of the molecule, the evidence supports an inference that 18F-labeled 4-APs can serve as PET tracers for demyelination.
Rats will be injected with LPC in the brain and spinal cord to create focal demyelinated areas at the sites of injection. 1-6 days after LPC injection, the rats will be injected intravenously with [14C] 3-F-4-AP (0.5 mg/kg, 0.5 uCi/g). 20-90 min after [14C] 3-F-4-AP injection, the rats will be euthanized and their brains removed. Thin sections of the brain will be prepared using a cryostat and mounted into glass slides. The slides will be then exposed to a radiation sensitive film for up to 6 weeks. After exposure, the film will be developed and the slides will be processed for IHC. The distribution of the drug on the brain revealed by autoradiographic signal and compared with the distrubution of myelin revealed by IHC. In some experiments, other 14C labeled fluorinated derivatives of 4-AP are used. In some experiments, 3H labeled fluorinated derivatives of 4-AP are used. In some embodiments, different rodent models of demyelination are used. In some embodiments, different species may be used.
The inventors will inject 0.005-50 mCi of [18F] 3-F-4-AP or other 18F-labeled 4-AP derivative into LPC treated rats. Immediately after injection of the tracer, dynamic emission scan will be performed in 3D acquisition mode on the animal using a GMI microPET/SPECT/CT system. In order to quantify the images, the signal will be integrated in the lesion and compare it to the signal in the same area in a control animal. The results will be analyzed using statistical tests. In some experiments, other 11C labeled fluorinated derivatives of 4-AP are used. In some embodiments, different rodent models of demyelination are used. In some embodiments, different species may be used. In some embodiments, the species will be humans.
The following references to the extent that they provide exemplary procedural or other details supplementary to those set forth herein.
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